Secondary Power Suply

Hi,
has someone attached a secondary power suply to a OM device ?
I am thinking of adding a solar cell to the back of the Freerunner.
So that if it lies around on my desk it will get the standby power by
the solar cell and not from the battery.
did someone tried something like that?
And did anyone know what the output V of the battery is?
(I haven't my freerunner jet. So i couldn't look into it. Is it 5V like
USB?)
Or maybe the mA of a stand by / full running Freerunner.
I know that we exceeded the 100mA at the boot up with glamo running.
(problem for the boot up without battery)
But in a stand by situation, we must be under 100mA because we could
charge the device with a 100mA usb device......
or am i completely wrong?
cu
Beni.